pulling slides on a piston tuba

[clintontuba2]

Is it true that, if you pull slides on a piston tuba without pressing the valves down, that you could expand the tubing of the horn? old rumor that i would like to know the truth to.

[Dan Schultz]

Is it true that, if you pull slides on a piston tuba without pressing the valves down, that you could expand the tubing of the horn? old rumor that i would like to know the truth to.

Old wive's tale.... urban legend.... take your pick. No truth to it.

[Lars Trawen]

Is it true that, if you pull slides on a piston tuba without pressing the valves down, that you could expand the tubing of the horn? old rumor that i would like to know the truth to.

Actually not, since you pull the slide a vacuum creates. If something occurs, the tube collapses. Fully thinkable, if you pull a slide fast enough, the vacuum could be deep enough to collapse the tube. Depending on how long the slide is and how tight the system is.
I've also heard about that and don't move a slide without depressing the appropriate valve, just to avoid any risk. However, I've never seen or heard it happens to anybody, so I agree with TubaTinker, it's most likely a rumor only.
By the way, why only on piston tubas? Rotary systems are well as tight as pistons.
There is another thing which concerns me more. The vacuum creates an airstream through the sealing parts of the valve. If particles are to come loose they will do it then. That could create future block.

[Dylan King]

I heard valve pulling causes cancer.

[Tubadork]

[Leland]

The only situation I've heard of where a vacuum can collapse a slide is with a trombone slide.

If you plug both ends and give it a strong yank, it's a pretty darned stiff vacuum. If the seal is well-lubed and the inner slide is thin and/or weak, it's conceivable that it could collapse.

[winston]

.

[Rick Denney]

While it will take several years, things do get a little looser if care is not taken to release the pressures. Piston valves use oil and then the water vapor to ride on in the valve casing. Continually pulling and not letting off the pressure will just make the valve a little looser over time.

Are you saying that because the vacuum pulls out the lubricant that the valve will wear more because of lack of lubricant? I'm not buying it. The valves would stick first.

On the original subject, let's do a little arithmetic. Let's say (since I'm too lazy to look it up), that the length of a first-valve slide is 20 inches with the slide all the way in, and let's say that the slide is 8 inches long. When the slide is at the point of falling out, the branch will be 36 inches in total length (20 + 2*8). If we take the amount of air held by that branch, and suddenly ram the slide home, we are compressing 36 inches of tubing worth of air into 20 inches of tubing. Since we started with air at atmospheric pressure, we end up with air at (36/20=) 1.8 times atmospheric pressure. Since the atmosphere pushes into the tube, it's only the .8 part that actually pushes on the tubing wall. That's 11 psi that the pipe has to resist (.8 times 14.7 psi, which is one atmosphere). (This calculation works the same way in vacuum, but the maximum possible vacuum is only 15 psi pushing on the tubing, which is 1 atmosphere outside the tube minus 0 atmospheres inside the tube.)

So, what's the yield pressure of the tube? Let's assume a .75" pipe, with a .02" wall thickness, made of brass that has a yield strength of 18,000 psi. The yield pressure is P = (2*S*T)/(O.D.-2*T), where S is the yield strength (in psi), T is the wall thickness and OD is outside diameter, both in inches. The yield pressure is therefore a little over 1000 psi.

1000 is a whole lot bigger than 11. "MYTH BUSTED!"

But it's useful to vent the valves anyway, because if you don't, you'll be producing percussion effects not written in the music when the pressure or vacuum is released.

(I'm intrigued by the trombone slide myth. If the slide is 36" long, it will have 72 inches of tubing in first position, and 132 inches of tubing in 7th (again just eyeballing it). Thus, 132/72 is 1.83 times atmospheric pressure, so the example is just like the one I chose above. But the tubing is smaller in diameter, making it stronger against pressure. I figure .02"-wall tubing of .5" in diameter will have a yield pressure of 1560 psi. That's a pretty darn good seal for a little light oil on the socks!)

(I'm also curious about Joe's claim that tubing that weak would crush if you tried to hold it. What wall thickness would correspond to 11 psi? The answer is 0.00023 inches, or about one-fourth the thickness of aluminum foil. Joe is right.)

Rick "who applied, but was rejected, for a job at Mythbusters" Denney

[Dan Schultz]

I heard valve pulling causes cancer.

I heard pulling your slides can cause blindness, too!

[Lew]

Once again Rick provides the scientific answer in a way that makes it clear without any question. Thanks. It makes me realize why I quickly moved to managing engineers rather than being one, even though I have the paper.

[Mark]

"MYTH BUSTED!"

Don't you just love that show?

[jacobg]

So why do people get their valves vented, then?

[Lew]

So why do people get their valves vented, then?

For this reason:

But it's useful to vent the valves anyway, because if you don't, you'll be producing percussion effects not written in the music when the pressure or vacuum is released.

Just to avoid the noise that can occur when you pull a slide then depress the valve.

[Dan Schultz]

So why do people get their valves vented, then?

The "New Thing" syndrome?

Funny.... the Miraphone 184 CC I have has all four valves vented. I don't understand why the former owner had it done because the first slide is the only one that is easy to get to. I'm not a slide-puller, anyway.

[clintontuba2]

i dont normally pull my slides to tune, i pull them to drain the water from the horn. I play a king 2341, which is a great horn. but the best way to drain the water is to just empty it via the tubing for each corresponding valve, it was frustrating at first, but once i got the hang of it, there are no problems.
to empty water from the 4th valve, you actually have to take the 4th valve slide out, and rotate the horn from the upright position counter-clockwise....took me a few weeks to figure it out. seems like trouble but it is worth it for this horn.

[Lee Stofer]

It is quite unlikely that any human could muster 10% of the PSI of vacuum needed to modify the shape of a slide.

I've been told that the most likely source of the rumor about slide-pulling causing damage if one didn't first depress the valve, has been salespersons who had instruments with no compression, and didn't want the prospective buyer to discover this. Hence, the warnings to never pull a slide without pressing the corresponding valve first have persisted. By the way, there are a lot of tubas out there that play OK, that have barely-perceptible compression at all. There are even some new tubas that fall into that category.

[Rick Denney]

Funny.... the Miraphone 184 CC I have has all four valves vented. I don't understand why the former owner had it done because the first slide is the only one that is easy to get to. I'm not a slide-puller, anyway.

Every CC Miraphone I've seen from the 70's and earlier had vented valves. It may be true of newer ones, too, but I haven't looked. BBb's didn't have vents. Most folks thought they were for applying oil.

It may be because pros tend to pull and dump to remove water, rather than making the noise of blowing through water keys. It's a lot easier to pull and dump if you don't have to worry about holding the valve button down. The only reason I've not done it on my Holton is that it's easy to hold open the (poorly placed) water key when pulling and dumping the slides.

Rick "who vented the valves on his Yamaha 621 just for this reason" Denney

[Dylan King]

The Yorkbrunner traps the most water of any horn I've played. I all eight slide and the spin once counter-clockwise to get all the spit out. I have never dropped a slide, but it is a careful procedure to avoid percussion sounds that aren't in the piece. So far, so good, but if my guitar playing carpel tunnel doesn't get better, I can see myself messing it up some day. Somebody needs to invent a device that evaporates the water as one plays.

[MaryAnn]

. Many horn players seem to have made this almost an art form

I had fun with this in a recent performance of Musical Joke. During the tacet movement I did some minor acrobatics emptying the horn, to audible giggles in the audience. I also had an audience member approach me after a concert once, asking why I spun the horn in the air that way.....and my first answer was "to make the audience ask questions" before I explained the water thing. I have a horn that won't empty unless I go through the "steering wheel routine" with it.
.....and, after you've done it several thousand times, it can start to resemble baton twirling.

MA

[Tubatoad]

I had always assumed that the vented valves in mirafones were as much to negate popping noise resulting from pressure change (warm air in the valve tuning cooling) as anything else. Bryan

For some reason this happened for the first time in my 40 years of horn (various) playing last Sunday. I warmed up my Cerveny, then had to stand outside in 45 degree weather for 5 minutes, then came back inside to play almost immediatly. I did a quick finger roll to warm the hand back up and was rewarded with what sounded like 4 rapid-fire farts. I gave the trombonist an odd look and I think he got the blame as we started to play right away! Never thought of this problem before, but I guess I better time my tube-venting more carefully in future.